In the present study, zeolite tuffs of diverse chemistry, mineralogy and origin were characterized and tested for their efficiency as slow release fertilizers (SRF) through a series of leaching tests. Mixtures of zeolite tuffs were created and tested as loamy soil additives, in order to evaluate any synergistic effect on their cation exchange capacity (CEC) and SRF properties. The studied materials were a chabazite-rich tuff (SOR), a mordenite-rich tuff (KIM), 3 mixtures of them (SOR/KIM 30/70, 50/50 and 70/30) and a commercial clinoptilolite-rich tuff (BLG). CEC (sodium acetate method) was 95.7 for BLG, 100.9 for KIM and 92.2 cmol kg -1 for SOR, while their mixtures displayed intermediate values. SRF values vary, with the SOR/KIM 30/70 exhibiting the slowest NH 4 + release in 29 days (1.7%) compared to the control sample (19%). Zeolites promoted PO 4 -3 release, while their selectivity for Mg 2+ and K + was clearly affected by their different structure and chemistry. BLG exhibited the strongest selectivity for Mg 2+ , having the lowest release (39%). The results demonstrate that mixtures of zeolite tuffs could have a potential use in agricultural processes, by improving parameters like: chemistry, mineralogy, CEC and SRF efficiency,and resulting in the production of a competitive and functional soil additive.

The aim of this paper is to evaluate the effects of natural and synthetic zeolitic materials as soil amendments in contaminated soils. Two species of natural zeolites, clinoptilolite and mordenite, sampled from Samos Island, Greece, were used as low-cost modifiers (amendments). Both of these materials show perfect XRD-patterns. Moreover, coal fly ash (CFA) derived from the electrostatic precipitators of the Meliti power plant (Florina, Greece) converted via an alkaline hydrothermal treatment with 1M NaOH was used to produce a synthetic zeolitic material. The mineralogical composition of natural and synthetic zeolites was tested and identified by X-ray diffraction (XRD) and scanning electron microscope (SEM). The amendments and original contaminated soils from a former mining area of Lavrion, were mixed and equilibrated for 1 week, hydrated up to 40% of their water holding capacity. After the equilibration, the growth of Trifolium alexandrinum both in amended and original soils was studied in a pot experiment. The increase in pH value of treated soil by the tested amendments, confirmed the buffering effect and suggested the opportunity of using zeolitic materials for conditioning and remedying contaminated acidic soils from sulphidic mining areas. Moreover, the amended soils exhibited higher CEC values compared with unamended soil. Results showed that the synthetic zeolite produced by Meliti’s power station fly ash, was the most effective for plant growth, among the tested amendments. Between natural zeolitic materials from Samos Island, the most efficient was the clinoptilolite rich, probably because of its better water holding capacity compared with mordenite.

The aim of this study is to examine the effectiveness of natural and synthetic zeolitic